Homopolymers and copolymers of ethylene

ABSTRACT

Ethylene homopolymers and copolymers having a broad molecular distribution, excellent toughness and improved processability are disclosed. These polymers may be prepared by use of a single metallocene catalyst system in a single reactor in the gas phase. These polymers of density typically 0.85-40.95 are defined in particular by their melt strength (MS) and long chain branching (LCB) characteristics and are particularly suitable for use in low density film applications.

[0001] The present invention relates to novel polymers and in particularto novel copolymers having a broad molecular weight distribution,toughness and improved processability.

[0002] In recent years there have been many advances in the productionof polyolefin copolymers due to the introduction of metallocenecatalysts. Metallocene catalysts offer the advantage of generally higheractivity than traditional Ziegler catalysts and are usually described ascatalysts which are single-site in nature. Because of their single-sitenature the polyolefin copolymers produced by metallocene catalysts oftenare quite uniform in their molecular structure. For example, incomparison to traditional Ziegler produced materials, they haverelatively narrow molecular weight distributions (MWD) and narrow ShortChain Branching Distribution (SCBD). Although certain properties ofmetallocene products are enhanced by narrow MWD, difficulties are oftenencountered in the processing of these materials into useful articlesand films relative to Ziegler produced materials. In addition, theuniform nature of the SCBD of metallocene produced materials does notreadily permit certain structures to be obtained.

[0003] An approach to improving processability has been the inclusion oflong chain branching (LCB), which is particularly desirable from theviewpoint of improving processability without damaging advantageousproperties. U.S. Pat. Nos. 5,272,236; 5,278,272; 5,380,810; and EP659,773, EP 676,421, relate to the production of polyolefins with longchain branching.

[0004] Another approach is the addition of the polymer processing aidsto the polymer prior to fabrication into films or articles. Thisrequires extra processing and is expensive.

[0005] A different approach to the problem has been to make compositionswhich are blends or mixtures of individual polymeric materials with theaim being to maximise the beneficial properties of given component whileminimising its processing problems. This also requires extra processingwhich increases the cost of materials produced. U.S. Pat. Nos.4,598,128; 4,547,551; 5,408,004; 5,382,630; 5,383,631; and 5,326,602;and WO 94/22948 and WO 95/25141 relate to typical blends.

[0006] Another way to provide a solution for the processability problemsand to vary SCBD has been the development of various cascade processes,where the material is produced by a series of polymerizations underdifferent reactor conditions, such as in a series of reactors.Essentially, a material similar in some ways to a blend is produced,with a modality greater than one for various physical properties, suchas the molecular weight distribution. While polyolefin compositions withsuperior processability characteristics can be produced this way, thesemethods are expensive and complicated relative to the use of a singlereactor. Processes of interest are disclosed in U.S. Pat. No. 5,442,018,WO 95/26990, WO 95/07942 and WO 95/10548.

[0007] Another potentially feasible approach to improving processabilityand varying SCBD has been to use a multicomponent catalyst. In somecases, a catalyst which has a metallocene catalyst and a conventionalZiegler-Natta catalyst on the same support are used to produce amultimodal material. In other cases two metallocene catalysts have beenused in polyolefin polymerizations. Components of different molecularweights and compositions are produced in a single reactor operatingunder a single set of polymerisation conditions. This approach isdifficult from the point of view of process control and catalystpreparation. Catalyst systems of interest are disclosed in WO 95/11264and EP 676,418.

[0008] WO96/04290 teaches the use of the preferred metallocene complexesof this invention to make ethylene copolymers. In particular, Examples44 and 45 teach the preparation of polymer using gas-phase techniques.The examples teach only operation for a hour or less in batch mode andno details of the original polymer bed composition is given.

[0009] U.S. Pat. No. 5,462,999 and U.S. Pat. No. 5,405,922 teaches thepreparation of ethylene copolymers in the gas-phase using a silicasupported metallocene catalyst. It is believed, however, that theproducts produced by following the examples will not contain long chainbranching and in particular will have lower values for the parametersδ(MS)/δ(P) and δ(MS)/δ(log{dot over (γ)}) than is claimed herein.

[0010] EP 676421 also teaches the preparation of copolymers in the gasphase sing a supported metallocene catalyst. The products produced inthe examples of this patent in general also have lower values for theparameters δ(MS)/δ(P) and δ(MS)/δ(logy) than is claimed herein.

[0011] EP 452920 and EP495099 teach the production of ethylenecopolymers using metallocene catalysts. Once again it is believed thatthe examples contained therein will not produce products with some orall of the desirable characteristics mentioned below

[0012] It would be desirable to be able to produce a polyolefincopolymer composition which is very easy to process and which isproduced using a single metallocene catalyst system preferably supportedin a polymerisation process using a single reactor, preferably gasphase, operating semi-continuously or, preferably, continuously under asingle set of reactor conditions.

[0013] It would also be desirable to produce polymers which have theprocessability and impact strength similar to highly branched lowdensity polyethylene (LDPE).

[0014] It would also be highly desirable to produce polymers having theabove properties which may be suitable for use in low densitypolyethylene film applications.

[0015] We have now found copolymers of ethylene and alpha olefins may beprepared which have improved processability and which exhibit specificmelt strength characteristics. Such copolymers are advantageouslyprepared using a single metallocene catalyst system using a singlegas-phase, fluidised bed reactor.

[0016] Thus according to a first aspect of the present invention thereis provided a copolymer of ethylene and one or more alpha olefinscontaining from three to twenty carbon atoms said copolymer having:

[0017] a) a long chain branching g′ value of less than or equal to 0.9and

[0018] b) a value of the derivative function δ(MS)/δ(P) of greater than0.6 wherein MS is the melt strength of the copolymer in cN and P is theextrusion pressure of the copolymer in MPa.

[0019] In a second aspect of the invention there is provided a copolymerof ethylene and one or more alpha olefins containing from three totwenty carbon atoms said copolymer having:

[0020] a) a long chain branching g′ value of less than or equal to 0.9and

[0021] b) a value of the derivative function δ(MS)/δ(logy) of greaterthan 7.5 wherein MS is the melt strength of the copolymer in cN and {dotover (γ)} is the shear rate of the copolymer in secs⁻¹.

[0022] Also provided by the present is a homopolymer of ethylene or acopolymer of ethylene and one or more alpha olefins containing fromthree to twenty carbon atoms said homopolymer or copolymer having:

[0023] a) a value of the derivative function δ(MS)/δ(P) of greater than0.6 and

[0024] b) an M_(w)/M_(n) value of in the case of the copolymer less than8 and in the case of the homopolymer less than 6

[0025] wherein MS is the melt strength of the copolymer or homopolymerin cN and P is the extrusion pressure of the copolymer or homopolymer inMPa and M_(w)/M_(n) is the ratio of weight average molecular weight tonumber average molecular weight of the copolymer or homopolymer asmeasured by gel permeation chromatography.

[0026] The derivative function value δ(MS)/δ(P) is preferably ≧0.75 andmore preferably ≧0.8.

[0027] In a further aspect of the present invention as herein describedthere is provided a homopolymer of ethylene or a copolymer of ethyleneand one or more alpha olefins containing from three to twenty carbonatoms said homopolymer or copolymer having:

[0028] a) a value of the derivative function δ(MS)/δ(logy) of greaterthan 7.5 and

[0029] b) an M_(w)/M_(n) value of less than 6.5 wherein MS is the meltstrength of the copolymer in cN and {dot over (γ)} is the shear rate ofthe copolymer in secs⁻¹ and M_(w)/M_(n) is the ratio of weight averagemolecular weight to number average molecular weight as measured by gelpermeation chromatography.

[0030] Another aspect of the present invention is provided by ahomopolymer of ethylene or a copolymer of ethylene and one or more alphaolefins containing from three to twenty carbon atoms said homopolymer orcopolymer having a long chain branching g′ value of between about 0.6and about 0.9. The homopolymers and copolymers of this aspect of theinvention may also have either or both of (a) a value of the derivativefunction δ(MS)/δ(P) of greater than 0.6 or (b) a value of the derivativefunction δ(MS)/δ(log{dot over (γ)}) of greater than 7.5 wherein MS isthe melt strength of the copolymer in cN and P is the extrusion pressureof the copolymer in MPa and {dot over (γ)} is the shear rate of thecopolymer in secs⁻¹.

[0031] The homopolymers and copolymers of the present invention whichare described above exhibit considerable rate advantages when processedfor commercial use. Thus relative to those products known to date thehomopolymers and copolymers of the present invention can be processed atlower melt temperature with lower melt pressure and lower powerconsumption than for previously known polymers of equivalent melt index.Alternatively for the same external conditions higher throughputs can beachieved.

[0032] The long chain branch parameter, g′ may be calculated from gelpermeation chromatography data (GPC) on-line viscometry data.

[0033] Although the present invention is not limited in all its aspectsto homopolymers and copolymers possessing long chain branches, it ispreferable that all the homopolymers and copolymers of the presentinvention have this feature. In such cases, the value of the long chainbranching parameter g′ for all the copolymers of the present inventionshould be less than 0.9, preferably less than 0.8, or alternativelypreferably greater than 0.5. Preferably the parameter lies in the rangeabout 0.5 to about 0.9 preferably in the range 0.55 to 0.85 morepreferably in the range about 0.6 to about 0.8 and most preferably inthe range 0.65 to 0.8. For the homopolymers the g′ parameter should bein the-range about 0.6 to about 0.9 more preferably 0.6 to 0.8 and mostpreferably 0.65 to 0.8.

[0034] As far as the melt strength (MS), extrusion pressure (P) andshear rate ({dot over (γ)}) parameters are concerned, the methods ofmeasuring these for polymers are well known to those skilled in the art.By measuring the MS parameter it is possible to construct for examplegraphical relationships which allow the two derivative functionsδ(MS)/δ(P) and δ(MS)/δ(log{dot over (γ)}) to be calculated. The meltstrength (MS) and extrusion pressure at shear rate of 500/S may also becalculated in this way. Although the present invention is not limited inall its aspects to homopolymers and copolymers in which either or bothof these derivative functions is a critical parameter, it is preferablethat all the homopolymers and copolymers of the present invention meetat least one and preferably both of the following numerical constraints.As far as the derivative function δ(MS)/δ(P) is concerned this should begreater than 0.6, desirably greater than 0.65, more desirably greaterthan 0.7 and most desirably greater than 0.80. Preferably the value ofthe derivative function δ(MS)/δ(P) should be in the range greater than0.6 to less than 1.5 more preferably from 0.65 to less than 1.4, evenmore preferably from 0.7 to 1.3 and most preferably from 0.8 to 1.2.

[0035] The derivative function δ(MS)/δ(log{dot over (γ)}) should begreater than 7.5 desirably 7.75 or greater and more desirably 8.0 orgreater. Preferably the value of this derivative function lies in therange greater than 7.5 to 15.0, more preferably from 7.75 to 13.0 andmost preferably 8.0 to 12.0.

[0036] The copolymers according to the present invention may also bedefined with respect to activation energy Ea as measured by dynamicrheometry. Thus according to another aspect of the invention there isprovided a copolymer of ethylene and one or more alpa olefins containingfrom three to twenty carbon atoms said copolymer having:

[0037] (a) an activation energy, Ea, of value greater than or equal to40 kJ/mol and

[0038] (b) a value of the derivative function δ(MS)/δ(P) of greater than0.6

[0039]  wherein MS is the melt strength of the copolymer in cN and P isthe extrusion pressure of the copolymer in MPa. Ea is measured bydynamic rheometry.

[0040] Preferably the value of the derivative function δ(MS)/δ(P) isgreater than 0.65 and most preferably greater than 0.75.

[0041] The derivative function may also be represented by therelationship

0.65≦δ(MS)/δ(P)≦1.4

[0042] and preferably

0.7≦δ(MS)/δ(P)≦1.2.

[0043] In a further aspect of the invention there is provided acopolymer of ethylene and one or more alpa olefins containing from threeto twenty carbon atoms said copolymer having:

[0044] (a) an activation energy, Ea of value greater than or equal to 40kJ/mol and

[0045] (b) a value of the derivative function δ(MS)/δ(log {dot over(γ)}) of greater than 7.5

[0046]  wherein MS is the melt strength of the copolymer in cN and γ isthe shear rate of the copolymer in sec⁻¹. Ea is measured by dynamicrheometry.

[0047] Preferably the value of the derivative function δ(MS)/δ(log{dotover (γ)}) is greater than 7.5 and most preferably greater than 8.0.

[0048] The derivative function may also be represented by therelationship

8.0≦δ(MS)/δ(log {dot over (γ)})≦12.

[0049] In normal polymer extrusion, for example in film processing, thethroughput rate is usually high and the corresponding shear rate isexpected to be in region of, or greater than, 500/s. The shear.viscosity η(500/s), extrusion pressure P(500/s) and melt strengthMS(500/s), measured at shear rate of 500/s, using both the capillaryrheometer and Rheotens, have thus been used to characterise theprocessability of polymer (Table 2). Although the present invention isnot limited in all its aspects to homopolymers and copolymers in whichthese parameters are critical, it is preferable that all thehomopolymers and copolymers of the present invention should have aMS(500/s) be greater than 13 cN desirably 15 cN and more desirably 16 cNor greater; a P(500/s) value should be less than or equal to 19 MPadesirably 18 MPa and more desirably 17.5 MPa or less; a η(500/s) shouldbe less than or equal to 430 Pa.s desirably 400 Pa.s and more desirably300 Pa.s or less.

[0050] In another aspect of the invention there is provided a copolymerof ethylene and one or more alpha olefins containing from three totwenty carbon atoms said copolymer having:

[0051] (a) a long chain branching g′ value of less than or equal to 0.9and

[0052] (b) a melt strength, MS(500/s) and extrusion pressure, P(500/s)satisfying the relationship:

MS(500/s)> or =P(500/s)−4.5

MS(500/s)> or =P(500/s)−4 desirably

MS(500/s)> or =P(500/s)−3.5 more desirably

[0053]  wherein MS is the melt strength of the copolymer in cN and P isthe extrusion pressure of the copolymer in MPa, all determined at shearrate of 500/s using a Rosand Capillary Rheometer and a GottfertRheotens.

[0054] In a further aspect of the invention there is provided acopolymer of ethylene and one or more alpha olefins containing fromthree to twenty carbon atoms said copolymer having:

[0055] (a) an activation energy, Ea, of value greater than or equal to40 kJ/mol and

[0056] (b) a melt strength, MS(500/s) and extrusion pressure, P(500/s)satisfying relationship:

MS(500/s)> or =P(500/s)−4.5

MS(500/s)> or =P(500/s)−4 desirably

MS(500/s)> or =P(500/s)−3.5 more desirably

[0057]  wherein MS is the melt strength of the copolymer in cN and P isthe extrusion pressure of the copolymer in MPa, all determined at shearrate of 500/s using a Rosand Capillary Rheometer and a GottfertRheotens. Ea is measured by dynamic rheometry.

[0058] Another aspect of the invention there is provided a copolymer ofethylene and one or more alpha olefins containing from three to twentycarbon atoms said copolymer having:—

[0059] (a) a melt strength, MS(500/s) and Mw/Mn value satisfyingrelationship:

MS(500/s)> or =1.13(Mw/Mn)+9.5, and

[0060] (b) a melt strength, MS(500/s) and extrusion pressure, P(500/s)satisfying relationship:

MS(500/s)> or =P(500/s)−4.5

MS(500/s)> or =P(500/s)−4 desirably

MS(500/s)> or =P(500/s)−3.5 more desirably

[0061]  wherein MS is the melt strength of the copolymer in cN and P isthe extrusion pressure of the copolymer in MPa, all determined at shearrate of 500/s using a Rosand Capillary Rheometer and a GöttfertRheotens. Mw/Mn is the ratio of weight average molecular weight tonumber molecular weight as measured by gel chromatography.

[0062] Another aspect of the invention there is provided a copolymer ofethylene and one or more alpha olefins containing from three to twentycarbon atoms said copolymer having:—

[0063] (a) a melt strength, MS(500/s) and Mw/Mn value satisfyingrelationship:

MS(500/s)> or =1.13(Mw/Mn)+9.5, and

[0064] (b) a melt strength, MS(500/s) and shear viscosity, η(500/s)satisfying relationship:

MS(500/s)> or =0.053η(500/s)−4.0

MS(500/s)> or =0.053η(500/s)−3.5 desirably

MS(500/s)> or =0.053η(500/s)−3.0 more desirably

[0065]  wherein MS is the melt strength of the copolymer in cN and η isthe shear viscosity of the copolymer in Pa.s, all determined at shearrate of 500/s using a Rosand Capillary Rheometer and a GottfertRheotens. Mw/Mn is the ratio of weight average molecular weight tonumber molecular weight as measured by gel chromatography.

[0066] The parameter M_(w)/M_(n) is calculated from corresponding valuesfor the weight average molecular weight M_(w) and the number averagemolecular weight M_(n) in turn obtained from gel permeationchromatography. Although the present invention is not limited in all itsaspects to homopolymers and copolymers in which this parameter iscritical, it is preferable that all the homopolymers and copolymers ofthe present invention should have an M_(w)/M_(n) value of less than 8preferably less than 7 more preferably less than 6.5 and most preferablyless than 6.

[0067] Turning to other characteristics of the homopolymers andcopolymers of the present invention, the density of these materialsshould be in the range 0.8 to 10.0 preferably 0.85 to 0.95 and mostpreferably 0.91 to 0.93. It is preferable that the melt flow ratio ofthe polymer measured at a load of 2.16 kg by standard techniques is inthe range 0.01 to 100 and more preferably in the range 0.1 to 10dg.min⁻¹. Typically the weight average molecular weight of the materialis in the range 25,000 to 500,00 preferably 50,000 to 250,000 and mostpreferably 80,000 to 200,000. For the copolymers of the presentinvention it is preferable that they are comprised of between 2 and 30weight %, most preferably between 5 and 20 weight % of units derivedfrom the precursor comonomer.

[0068] The most preferable homopolymers and copolymers of the presentinvention appear to be characterised by molecular weight distributions(as measured by gel permeation chromatography) which show varyingdegrees of deviation from unimodality. In some instances these nonunimodal characteristics are manifested in clear bimodality or even morecomplex distributions indicative of even higher orders of modality. Thisproperty is one which in particular has been seen before in connectionwith single site catalyst operating in a single reaction environment.

[0069] The homopolymers and copolymers of the present invention aresuitably prepared by continuous polymerisation of the requiredmonomer(s) in the presence of a single metallocene catalyst system in asingle reactor. By the term continuous polymerisation is meant a processwhich for at least a significant period of time is operated withcontinuous feeding of the monomer(s) to the reactor in parallel withcontinuous or periodic withdrawing of homopolymer or copolymer product.Preferably the continuous polymerisation is effected in the gas phase atelevated temperature in the presence of a fluidised bed of polymerparticles and continuous recycle of unreacted monomer(s) around a loopjoining the inlet and outlet of the reactor containing the fluidisedbed. Examples of two possible approaches are described in EP 89961, U.S.Pat. No. 5,352,7947 and U.S. Pat. No. 5,541,270 the complete texts ofwhich are herein incorporated by reference. EP 699213 also illustrates apossible approach and again the complete text of this publication isincorporated by reference. The metallocene catalyst system comprises ametallocene complex and activating cocatalyst which in the case of a gasphase process is preferably supported on an inert carrier (e.g. silica).The catalyst system can be optionally prepolymerised and/or utilised inthe presence of a Group IIIa metal alkyl scavenger such as an aluminiumalkyl.

[0070] Suitable metallocene complexes which can be used to prepare thehomopolymers and copolymers of the present invention comprise thoseorganometallic complexes of the Group IVB (i.e. the titanium group)having between one and three η⁵ bonded cylopentadienyl indenyl orfluorenyl ligands. Whilst these ligands may be unsubsituted orsubstituted at one or more of their carbon atoms with a substituent,including but not limited to alkyl groups having from one and ten carbonatoms, the most preferred metallocene complexes are those where at leasttwo of the cyclopentadienyl, indenyl and fluorenyl ligands are connectedtogether by a divalent bridging group e.g. an alkylene group having fromone to eight carbon atoms or the corresponding silylene, germanylenederivatives. These alkylene, silylene and germanylene groups can in turnbe substituted on the carbon and silicon backbone. Alternativelybridging can be effected by using a divalent phoshino or amino group thethird valence of each being satisfied by an alkyl group having betweenone and eight carbons or phenyl (either substituted or unsubstituted).

[0071] The indenyl or fluorenyl ligands in such complexes may also be inthe form of their hydrogenated derivatives.

[0072] Most preferred metallocene complexes are those having thefollowing general formula:

[0073] wherein

[0074] M is titanium, zirconium or hafnium,

[0075] D is a stable conjugated diene optionally substituted with one ormore hydrocarbyl groups, silyl groups, hydro carbylsily groups,silylhydrocarbyl groups or mixtures thereof, or may contain a Lewis basefunctionality, said D having from 4 to 40 non-hydrogen atoms and forminga π-complex with M,

[0076] Z is a bridging group comprising an alkylene group having 1-20carbon atoms or a dialkyl silyl- or germanyl group or alkyl phosphine oramino radical,

[0077] R is hydrogen or alkyl having from 1-10 carbon atoms, and x is1-6.

[0078] Most preferred metallocene complexes in this family are thosewhere, as evidenced by X-ray diffraction or NMR, the D ligand isπ-bonded to the M atom in an η³ fashion. Such metallocene complexes arecharacterised by the M atom being in the +2 oxidation state.

[0079] Preferred complexes are those wherein M is zirconium and Z isethylene (CH₂CH₂).

[0080] The D ligand is most preferably chosen from the group:

[0081] s-trans-η⁴,4-diphenyl-1,3-butadiene;s-trans-η⁴-3-methyl-1,3-pentadiene;s-trans-η⁴-1,4-dibenzyl-1,3-butadiene; s-trans-η⁴-2,4-hexadiene;s-trans-η⁴-1,4-ditolyl-1,3-butadiene;s-trans-η⁴-1,4-bis(trimethylsilyl)-1,3-butadiene;scis-η⁴-1,4-diphenyl-1,3-butadiene; s-cis-η⁴-3-methyl-1,3-pentadiene;s-cis-η⁴-2,4-hexadiene; s-cis-η⁴2,4-hexadiene; s-cis-η⁴1,3-pentadiene;s-cis-η⁴-1,4-ditolyl-1,3-butadiene; ands-cis-η⁴-1,4-bis(trimethylsilyl)-1,3-butadiene, said s-cis diene groupforming a π-complex as defined herein with the, metal.

[0082] Particularly suitable are externally substituted dienes inparticular the 1,4-diphenyl substituted butadienes.

[0083] The preparation of these complexes is extensively described in WO96/04290 which also lists examples of suitable representatives for usein the present invention.

[0084] When the diene group D has a Lewis base functionality this may bechosen from the following groups:

[0085] —NR₂, —PR₂, —AsR₂, —OR, —SR

[0086] Particularly preferred dienes of this type are dialkylarminophenyl substituted dienes for example 1-phenyl-4 (N,N′-diethylaminophenyl) 1,3-butadiene.

[0087] The most preferred complex is ethylene bis(indenyl) zirconium(II) 1,4-diphenyl butadiene having the following formula:—

[0088] Also preferred is the hydrogenated analogue-ethylenebis(tetrahydroindenyl) zirconium (II) 1,4-diphenyl butadiene.

[0089] The activating cocatalysts suitable for use with the abovemetallocene complexes are preferably tri(hydrocarbyl) boranes inparticular trialkylboranes or triarylboranes. Most preferred cocatalystsare perfluorinated tri(aryl) boron compounds and most especiallytris(pentafluorophenyl) borane. Other activators include borate salts ofa cation which is a Bronsted acid capable of donating a proton to one ofthe ligands on the metallocene complex. The potential scope of boththese types of activators is illustrated in WO 96/04290 the relevantsections of which are herein incorporated by reference.

[0090] Another type of activator suitable for use with the metallocenecomplexes of the present invention are the reaction products of (A)ionic compounds comprising a cation and an anion wherein the anion hasat least one substituent comprising a moiety having an active hydrogenand (B) an organometal or metalloid compound wherein the metal ormetalloid is from Groups 1-14 of the Periodic Table.

[0091] Suitable activators of this type are described in WO 98/27119 therelevant portions of which are incorporated by reference.

[0092] A particular preferred activator of this type is the reactionproduct obtained from alkylammonium tris(pentafluorophenyl)4-(hydroxyphenyl) borates and trialkylamines. For example a preferredactivator is the reaction product of bis(hydrogenated tallow alkyl)methyl ammonium tris (pentafluorophenyl) (4-hydroxyphenyl) borate andtriethylamine.

[0093] The molar ratio of metallocene complex to activator employed inthe process of the present invention may be in the range 1:10000 to100:1. A preferred range is from 1:5000 to 10:1 and most preferred from1:10 to 10:1.

[0094] The metallocene catalysts system suitable for use in the presentinvention is most suitably supported. Typically the support can be anyorganic or inorganic inert solid. However particularly porous supportssuch as talc, inorganic oxides and resinous support materials such aspolyolefins which have well-known advantages in catalysis are preferred.Suitable inorganic oxide materials which may be used include Group 2,13, 14 or 15 metal oxides such as silica, alumina, silica-alumina andmixtures thereof Other inorganic oxides that may be employed eitheralone or in combination with the silica, alumina or silica-alumina aremagnesia, titania or zirconia. Other suitable support materials may beemployed such as finely divided polyolefins such as polyethylene.

[0095] The most preferred support material for use with the supportedcatalysts according to the process of the present invention is silica.Suitable silicas include Crossfield ES70 and Davidson 948 silicas.

[0096] It is preferable that the silica is dried before use and this istypically carried out by heating at elevated temperatures for examplebetween 200 and 850 deg. C.

[0097] In another aspect of the present invention homopolymers ofethylene or copolymers of ethylene and one or more alpha-olefinscontaining from three to twenty carbon atoms may be prepared in thepresence of a single metallocene catalyst comprising a metallocenecomplex and an activating cocatalyst wherein the activating cocatalystis not an alkyl aluminoxane for example methyl aluminoxane (MAO).

[0098] In such cases there is thus provided a copolymer of ethylene andone or more alpha-olefins containing from three to twenty carbon atomssaid copolymer having:

[0099] (a) a long chain branching g′ value of less than or equal to 0.9and

[0100] (b) a value of the derivative function δ(MS)/δ(log {dot over(γ)}) and a Mw/Mn satisfy the relationship:

log[δ(MS)/δ(log {dot over (γ)})]≧0.6 log(Mw/Mn)+0.3

[0101]  wherein Mw/Mn is the ratio of weight average molecular weight tonumber molecular weight as measured by gel chromatography.

[0102] Such polymers may also be defined by:—

[0103] (a) a long chain branching g′ value of less than or equal to 0.9and

[0104] (b) a value of the derivative function δ(MS)/δ(P) and Mw/Mn whichsatisfy the relationship:

δ(MS)/δ(P)≧0.12 Mw/Mn

[0105]  wherein Mw/Mn is the ratio of weight average molecular weight tonumber molecular weight as measured by gel chromatography.

[0106] The polymers may also be defined with respect to the flowactivation energy Ea as follows:—

[0107] (a) an flow activation energy, Ea, of value greater than or equalto 40 kJ/mol and

[0108] (b) a value of the derivative function δ(MS)/δ(log {dot over(γ)}) and a Mw/Mn which satisfy the relationship:

log[δ(MS)/δ(log {dot over (γ)})]≧0.6 log(Mw/Mn)+0.3

[0109]  wherein Mw/Mn is the ratio of weight average molecular weight tonumber molecular weight as measured by gel chromatography. Ea ismeasured by dynamic rheometry. Alternatively the polymers may be definedby:

[0110] (a) an flow activation energy, Ea, of value greater than or equalto 40 kJ/mol and

[0111] (b) a value of the derivative unction δ(MS)/δ(P) and Mw/Mn whichsatisfy the relationship:

δ(MS)/δ(P)≧0.12 Mw/Mn

[0112]  wherein Mw/Mn is the ratio of weight average molecular weight tonumber molecular weight as measured by gel chromatography. Ea ismeasured by dynamic rheometry.

[0113] The polymer may be defined by:

[0114] (a) a long chain branching g′ value of less than or equal to 0.9and

[0115] (b) a value of the derivative function δ(MS)/δ(P) and a flowactivation energy Ea satisfy the relationship:

Log[δ(MS)/δ(P)]≧3.7−2.4 log(Ea)

[0116]  wherein Ea is measured by dynamic rheometry.

[0117] Such polymers may also be defined by:

[0118] (a) a long chain branching g′ value of less than or equal to 0.9and

[0119] (b) a value of the derivative function δ(MS)/δ(log{dot over (γ)})and a flow activation energy Ea satisfy the relationship:

Log[δ(MS)/δ(log{dot over (γ)})]≧2.75−1.25 log(Ea)

[0120]  wherein Ea is measured by dynamic rheometry.

[0121] The copolymers of the present invention are copolymers ofethylene with one or more alpha-olefins having from three to twentycarbon atoms. Preferably the alpha-olefin has between three and tencarbon atoms most preferably three and eight. Examples of the mostpreferred alpha olefins include 1-butene, 1-hexene, 4-methyl-1-pentene,1-octene. Particular suitable are copolymers of ethylene with 1-hexeneor 4-methyl-1-pentene.

[0122] Fabricated articles made from the novel polymers of the presentinvention may be prepared using conventional polyolefin processingtechniques. Suitable articles of this type include film (eg cast, blownetc) fibres and moulded articles (eg produced using injection moulding,blow moulding or rotomoulding processes).

[0123] Other useful compositions are also possible comprising the novelpolymers of the present invention and at least one other natural orsynthetic polymer. Such compositions may be formed by conventionalmethods for example dry blending. Other suitable processing techniquesmay be used to prepare such compositions comprising the novel polymersof the present invention.

[0124] The novel polymers of the present invention may suitably be usedfor the manufacture of films and specific details of the film propertiesand given below in the examples.

[0125] In particular the novel polymers of the present invention may beused to prepare films having a dart impact value as measured by ASTM D1709 (method A) of greater than 100 and up to about 2000. Such filmscomprise copolymers of the invention of density 0.910-0.930, a I₂₁/O₂value of ≧35 and a long chain branching g¹ value of less than or equalto 0.9. In addition the copolymers exhibit the melt strengthcharacteristics defined in detail above.

[0126] In particular they exhibit a value of the derivative functionδ(MS)/δ(P) of >0.6. Alternatively they may also exhibit a value of thederivative function δ(MS)/δ(P) and flow activation Ea of

log[δ(MS)/δ(P)]≧3.7−2.4 log Ea.

[0127] Such polymers also exhibit a flow activation Ea of ≧40.

[0128] The present invention will now be further illustrated withreference to the following examples and Figures which represent thepreparation of copolymers according to the present invention and acomparison with commercially available prior art materials.

[0129]FIG. 1 shows the variation in melt strength (MS) with extrusionpressure at 190° C.

[0130]FIG. 2 shows the variation in melt strength (MS) with shear rateat 190° C.

[0131]FIG. 3 shows the variation in δ(MS)/δ(P) with melt flow rate (2.16Kg) at 190° C.

[0132]FIG. 4 shows the variation in δ(MS)/δ(log{dot over (γ)}) with meltflow rate (2.16 Kg) at 190° C.

[0133]FIG. 5 shows the variation in δ(MS)/δ(P) with M_(w)/M_(n) at 190°C.

[0134]FIG. 6 shows the variation in the δ(MS)/δ(log{dot over (γ)}) withM_(w)/M_(n) at 190° C.

[0135]FIG. 7 shows the variation in δ(MS)/δ(P) with the long chainbranching parameter g′ at 190° C.

[0136]FIG. 8 shows the variation in δ(MS)/δ(log{dot over (γ)}) with thelong chain branching parameter g′ at 190° C.

[0137]FIG. 9 shows the variation in δ(MS)/δ(P) with flow activationenergy (Ea) at 190° C.

[0138]FIG. 10 shows the variation in δ(MS)/δ(log{dot over (γ)}) withflow activation energy (Ea) at 190° C.

[0139] Table 2 sets out a range of relevant physical information forseven examples according to the present invention and examples of elevencommercially available or representative prior art materials.

[0140] The terms ‘Exceed’, ‘Affinity’, and ‘Dowlex’ are registered trademarks and herein recognised as such. Affinity FM1570, Exceed ML27MAX,Exceed 350D60, Dowlex 2045, NTA 101, LL7206AF, LL7209AA, LD 5320AA, LD531AA, and Borealis LE 6592 are all commercially available productswhose origin will be known to those skilled in the art. EBI/Zr(IV)/MAOis an experimental material produced according to EP 676421.

[0141] The following analytical procedures were used in order tocharacterise the novel polymers of the present invention and to comparesaid polymers with the prior art and commercially available materials.

[0142] 1. Rheological Characterisation

[0143] 1.1 Capillary Rheometry

[0144] The shear capillary viscosities of the polymers were measured at190° C., using a Rosand RH 7 twin-bore capillary rheometer, with two 1.0mm diameter dies: one with die length of 16 mm while the other has a(zero) die length of 0.25 mm. The die entry angle for both dies is 190°.All data are corrected for the effects of die entry & exit pressures(Bagley correction) and of non-Newtonian flow (Rabinowitsch correction).The shear viscosity at shear rate of 500/S, η(500/S) is then extractedfrom the corrected flow curve.

[0145] 1.2 Rheotens Extensional Rheometry

[0146] The melt strength of the polymer is measured at 190° C., using aGottfert Rheotens extensional rheometer in conjunction with a Rosand RH7 Capillary Rheometer. This is achieved by extruding the polymer at aconstant pressure (P) through a die of 1.5 mm diameter and 30 mm inlength, with a 90° entry angle. Once a given extrusion pressure isselected, the piston of the capillary rheometer will travel through its15 mm diameter barrel at a speed that is sufficient to maintain thatpressure constant using the constant pressure system of the rheometer.The nominal wall shear rate ({dot over (γ)}) for a given extrusionpressure can then be computed for the polymer at the selected pressure.

[0147] The extrudate is drawn with a pair of gear wheels at anaccelerating speed (V). The acceleration ranges from 0.12 to 1.2 cm/s²depending on the flow properties of the polymer under test. The drawingforce (F) experienced by the extrudate is measured with a transducer andrecorded on a chart recorder together with the drawing speed. Themaximum force at break is defined as melt strength (MS) at a constantextrusion pressure (P) or at its corresponding extrusion rate (γ). Threeor four extrusion pressures (6, 8, 12, 16 MPa) are typically selectedfor each polymer depending on its flow properties. For each extrusionpressure, a minimum of 3 MS measurements are performed and an average MSvalue is then obtained.

[0148] The derivative functions of the extrusion pressure and shear ratedependent melt strengths, δ(MS)/δ(P) and δ(MS)/γ(log {dot over (γ)}),for each polymer are computed from the slopes (by a least square linefitting) of the plots of the average MS against pressure and againstshear rate respectively. The melt strength and extrusion pressure atshear rate of 500/s, (MS(500/s), P(500/s) respectively, were alsocomputed from these plots. (See FIGS. 1-2).

[0149] 1.3 Melt Flow Rate (2.16 kg)

[0150] The melt flow rate (MFR) of the polymers was measured underconditions which conform to ISO 1133 (1991) and BS 2782:PART 720A:1979procedures. The weight of polymer extruded through a die of 2.095 mmdiameter, at a temperature of 190° C., during a 600 second time periodand under a standard load of 2.16 kg is recorded.

[0151] 2 Molecular Structure Characterisation

[0152] Various techniques (eg ¹³C NMR, GPC/LALLS, GPC/intrinsicviscosity, GPC/on-line viscometry and Theological flow activationenergy, etc) have been developed to indicate the presence of long chainbranching in polymers.

[0153] 2.1 Molecular Weight Distribution (M_(w)/M_(n)) and Long ChainBranching (LCB) Measurements by GPC/On-Line Viscometry.

[0154] Molecular weight distribution was determined by gel permeationchromatography/on-line viscometry (GPC/OLV) using a Waters 150CV. Themethod followed was based upon that described by J. Lesec et al, Journalof Liquid Chromatography, 17, 1029 (1994). It is well known to thoseskilled in the art that this technique can provide an estimate of longchain branching (LCB) content as a function of molecular weight. Whileit is possible to interpret the data in terms of the number of longchain branches per 1000 carbon atoms, an alternative approach is tointerpret the data in terms of the parameter g′ which is the ratio ofthe measured intrinsic viscosity to that of a linear polymer having thesame molecular weight. Linear molecules show g′ of 1, while values lessthan 1 indicate the presence of LCB. As always, the reliability of LCBdeterminations can be greatly strengthened by combining results fromseveral techniques rather then relying on a sole method.

[0155] Average values of g′ were calculated from the equation<g′>_(LCB)=[η]/[η]_(lin) where [η]=Σ(w_(i)[η]_(i), and[η]_(lin)=Σ(w_(i)[η]_(i,lin)

[0156] where w_(i) is the weight fraction, [μ]_(i) are measuredintrinsic viscosities of the long chain branched polymer fractions, and[η]_(i,lin) are the intrinsic viscosities of the equivalent linearpolymers of the same molecular weight for each slice, all calculatedfrom the slice data of the GPC/OLV experiment. The averaging was carriedout over the range of molecular weight for which reliable measures of[η]_(i) could be made. The data were not corrected for any contributionto g′ due to short chain branching. A molecular weight distributioncorrected for LCB and molecular weight averages corrected for LCB werecalculated in the normal manner. For some analyses of polymers known notto contain LCB the on-line viscometer was not used and uncorrected dataare reported and hence for these no <g′>LCB value is given.

[0157] Flow Activation Energy (E) Measurement

[0158] Rheological measurements were carried out on a Rheometrics RDS-2with 25 mm diameter parallel plates in the dynamic mode. Two strainsweep (SS) experiments were initially carried out to determine thelinear viscoelastic strain that would generate a torque signal which isgreater than 10% of the full scale (2000 g-cm) of the transducer overthe full frequency (eg 0.01 to 100 rad/s) and temperature (eg 170° to210° C.) ranges. The first SS experiment was carried out at the highesttest temperature (eg 210° C.) with a low applied frequency of 0.1 rad/s.This test is used to determine the sensitivity of the torque at lowfrequency. The second experiment was carried out at the lowest testtemperature (eg 170° C.) with a high applied frequency of 100 rad/s.This is to ensure that the selected applied strain is well within thelinear viscoselastic region of the polymer so that the oscillatoryTheological measurements do not induce structural changes to the polymerduring testing. This procedure was carried out for all the samples.

[0159] The bulk dynamic Theological properties (eg G′, G″ and η*) of allthe polymers were then measured at 170°, 190° and 210° C. At eachtemperature, scans were performed as a function of angular shearfrequency (from 100 to 0.01 rad/s) at a constant shear strainappropriately determined by the above procedure.

[0160] The dynamic Theological data was then analysed using theRheometrics RHIOS V4.4 Software. The following conditions were selectedfor the time-temperature (t-T) superposition and the determination ofthe flow activation energies (Ea) according to an Arrhenius equation,a_(T)=exp(E_(a)/kT), which relates the shift factor (a_(T)) to E_(a):Rheological Parameters: G′(ω), G″(ω) & η*(ω) Reference Temperature: 190°C. Shift Mode: 2D (ie horizontal & vertical shifts) Shift Accuracy: HighInterpolation Mode: Spline

[0161] The copolymers of the present invention may also be describedwith reference to melt flow ratio which is the ratio of I₂₁/I₂ whereinI₂₁ is measured at 190° C. in accordance with ASTM-D-1238 Condition E.

[0162] Copolymers according to the invention have a I₂₁/I₂ value of ≧35,preferably ≧40.

EXAMPLE 1 Preparation and Use of Zr (II) Polymerisation Catalyst

[0163] (i) Treatment of Silica

[0164] A suspension of Crossfield ES70 silica (20 kg, previouslycalcined at 500° C. for 5 hours) in 110 litres of hexane was made up ina 240 litre vessel under nitrogen and 3.0 g of Stadis 425 (diluted in 1litre hexane) was added. A solution of TEA in hexane (30.0 moles, 0.940Msolution) was added slowly to the stirred suspension over 30 minutes,while maintaining the temperature of the suspension at 30° C. Thesuspension was stirred for a further 2 hours. The hexane was decanted,and the silica washed with hexane, so that the aluminium content in thefinal washing was less than 1 mmol Al/litre. Finally the suspension wasdried in vacuo at 60° C. to give a free flowing treated silica powder.

[0165] (ii) Production of Catalyst

[0166] Toluene dried over molecular sieves (350 ml) was added to 10 g ofthe treated silica powder in a large Schlenk tube in a dry nitrogenglove box. The tube was shaken well to form a suspension and left tostand for 1 hour. To the suspension was added a solution oftris(pentafluorophenyl)boron in toluene (11.3 ml, 7.85 wt. %, d=0.88g/ml) by syringe. Then rac ethylene bis indenyl zirconocene 14 diphenylbutadiene (0.845 g) was added. The suspension was shaken well for 5minutes, then dried in vacuo at ambient temperature to give afree-flowing pink/red powder.

[0167] (iii) Gas-Phase Fluidised Bed Production of an Ethyene/Hexene-1Copolymer

[0168] Ethylene, hexene-1, hydrogen and nitrogen were polymerised usinga 15 cm diameter continuous fluidised bed reactor system. Polymerproduct was removed at regular intervals from the reactor. Operatingconditions are given in Table 1. The product was a white free flowingpowder.

EXAMPLES 2 AND 3 Preparation and Use of Zr(II) Catalysts

[0169] (i) Treatment of the Silica Support

[0170] 110 litres of hexane was placed in a 240 litre vessel undernitrogen and 1.7 g of Stadis 425 (diluted at 1 wt. % in hexane) wasadded. 11 kg of ES70 Crossfield silica (previously dried at 500° C. for5 hours) was then added. 16.5 moles of TEA (0.87 mole in hexane) wasthen added at 30° C. during a period of 30 minutes. After a holdingperiod of 2 hours, the hexane was decanted and the silica was washed 6times with 130 litres of hexane.

[0171] (ii) Production of the Catalyst

[0172] The silica treated as above was dried and then 38 litres oftoluene added. 11.7 kg of rac ethylene bis indenyl zirconocene 1-4diphenyl butadiene solution in toluene (1.32 wt %) was added at ambienttemperature during a period of 15 minutes. 0.7 g of Stadis 425 (dilutedat 1 wt % in toluene) was added The catalyst was then dried under vacuum(4 mmHg) at 40° C. to give a free flowing powder.

[0173] Then 2.33 kg of tris pentafluorophenyl boron solution (6.12 wt %in toluene) was added at ambient temperature during a period of 2 hourswhile maintaining continuous agitation. After a holding period of 1 houragain maintaining agitation a pink/red catalyst having residual solventtherein was obtained.

[0174] (iii) Gas-Phase Fluidised Bed Production of an Ethylene/Hexene-1Copolymer

[0175] Ethylene, hexene-1, hydrogen and nitrogen were fed into a 45 cmdiameter continuous fluidised bed reactor. Polymer product wascontinuously removed from the reactor. Operating conditions are given inTable 1:

EXAMPLE 4

[0176] (i) Treatment of Silica

[0177] A suspension of ES70 silica (16 kg, previously calcined at 500°C. for 5 hours) in 110 litres of hexane was made up in a 240 litrevessel under nitrogen. 1.7 g of Stadis 425 diluted in 1 L of hexane wasadded. A solution of TEA in hexane (24.0 moles, 1.0M solution) was addedslowly to the stirred suspension over 30 minutes, while maintaining thetemperature of the suspension at 30° C. The suspension was stirred for afurther 2 hours. The hexane was filtered, and the silica washed withhexane, so that the aluminium content in the final washing was less than1 mmol Al/litre. Finally the suspension was dried in vacuo at 60° C. togive a free flowing treated silica powder.

[0178] (ii) Catalyst Fabrication

[0179] 41.6L of toluene was added to the above treated silica powder.12.67 kg of rac ethylene bis indenyl zirconocene 14 diphenyl butadienesolution in toluene (1.16 wt %) was added at ambient temperature duringa period of 15 min then kept at 25° C. for 15 min. 50 ppm of Stadis 425diluted in 1L of toluene was added. The catalyst was then dried undervacuum at 40° C. to give a free flowing powder. Then 2.22 Kg oftris(pentafluorophenyl)boron solution in toluene (6.12 wt %) was addedat ambient temperature during a period of 2 hours while maintainingcontinuous agitation After a holding period of 1 h again maintainingagitation a catalyst having residual solvent therein was obtained.

[0180] (iii) Gas Phase Fluidised Bed Production of an Ethylene-Hexene-1Copolymer

[0181] The polymerisation was carried out as for Example 1, underconditions summarised in Table 1

EXAMPLE 5

[0182] (i) Treatment of Silica

[0183] 26.24 Kg of TEA treated ES70 silica was prepared in a dryer undernitrogen essentially as described in Example 4.

[0184] (ii) Catalyst Fabrication

[0185] 10 litres of 0.0809M solution in toluene of bis(hydrogenatedtallow alkyl) methyl ammoniumtris(pentafluorophenyl)(4-hydroxyphenyl)borate, was mixed with 0.9litres of TEA (1.01M) in toluene. The mixture was added to the treatedsilica with agitation and allowed to mix for 45 minutes. The solvent wasremoved during 1 hour under vacuum at a temperature of 31° C. 25 litresof 0.021M rac ethylene bis indenyl zirconocene 1-4 diphenyl butadiene intoluene was added and allowed to mix for 45 minutes. The solvent wasremoved during 105 minutes under vacuum at 34° C. The finished catalystwas steel-grey in colour and contained less than 0.25% residual solvent.

[0186] (iii) Gas Phase Fluidised Bed Production of an Ethylene-Hexene-1Copolymer

[0187] The polymerisation was carried out as for Examples 2 and 3, underconditions summarised in Table 1

EXAMPLE 6

[0188] (i) Treatment of Silica Support

[0189] A suspension of ES70 silica (16 kg, previously calcined at 500°C. for 5 hours) in 110 litres of hexane was made up in a 240 litrevessel under nitrogen. 1.7 g of a solution of Stadis 425 (in 1 litre ofhexane) was added. A solution of TEA in hexane (24.0 moles, 0.838Msolution) was added slowly to the stirred suspension over 30 minutes,while maintaining the temperature of the suspension at 30° C. Thesuspension was stirred for a further 2 hours. The hexane was filtered,and the silica washed with hexane, so that the aluminium content in thefinal washing was less than 0.5 mmol Al/litre. Finally the suspensionwas dried in vacuo at 60° C. to give a free flowing treated silicapowder.

[0190] (ii) Production of the Catalyst

[0191] All manipulations were done under an inert nitrogen atmosphere ina dry box. To 64.5 mL of a 0.073M solution in toluene ofbis(hydrogenated tallow alkyl) methyl ammoniumtris(pentafluorophenyl)(4-hydroxyphenyl)borate, was added 20.8 mL of0.25 M Et₃Al in toluene. 84.7 mL of this mixture was quantitativelyadded to 150 g of treated silica in a 3 L Round bottom flask and theresulting mixture was agitated for 30 min at ambient temperature. Thesolvent was removed under vacuum at 30° C. to the point where no furtherevolution of volatiles was observed. Immediately after, 138.3 mL of0.017M rac ethylene bis tetrahydro indenyl zirconocene 1-4 diphenylbutadiene in toluene were added and the powder was again agitated for 30min at ambient temperature. The solvent was removed under vacuum atambient temperature to the point where no further evolution of volatileswas observed.

[0192] (iii) Gas Phase Fluidised Bed Production of an Ethylene-Hexene-1Copolymer

[0193] The polymerisation was carried out as for Example 1, underconditions summarised in Table 1

EXAMPLE 7

[0194] All manipulations were done under an inert nitrogen atmosphere ina dry box.

[0195] (i) Treatment of Silica

[0196] Twenty grams of Crosfield ES-70 silica that were calcined in airat 500° C. were accurately weighed into a 250 mL Schlenk flask. 125 mLof hexane were added to make a slurry. 30.8 mL of 1.0 M TEA in hexanewere added while swirling the flask by hand and the flask was left tostand for 1 hour. The treated silica was filtered on a flit and washedwith several volumes of hexane. The silica was dried to constant weightunder vacuum at ambient temperature. 21.7 g of treated silica wererecovered

[0197] (ii) Production of Catalyst

[0198] Two grams of the above treated silica were accurately weighedinto a 100 mL Schlenk flask and 8 cc of toluene were added to make aslurry. 2.4 mL of 0.017 M rac ethylene bis tetrahydro indenylzirconocene 1-4 diphenyl butadiene in toluene and 0.5 mL of 0.127 Mtris(pentafluorophenyl)boron were added, in that order, while swirlingthe flask by hand. The solvent was-removed till constant weight, undervacuum at ambient temperature. 1.9 g of catalyst powder were recovered.

[0199] (iii) Gas Phase Production of an Ethylene-Hexene-1 Copolymer

[0200] The polymerisation was carried out in a 2.5-litre stirred, fixedbed autoclave. This was charged with 300 g dry NaCl, and stirring wasbegun at 300 rpm. The reactor was pressurised to 8.39 bar ethylene thatcontained 500 ppm volume of hydrogen and heated to 71° C. 1-hexene wasintroduced to a level of 6000 ppm volume as measured on a massspectrometer. 0.5 g of TEA was introduced into the reactor. In aseparate vessel, 0.1 g catalyst was mixed with an additional 0.5 g TEAtreated silica. The combined catalyst and TEA treated silica weresubsequently injected into the reactor. Ethylene pressure was maintainedon a feed as demand, and hexene was fed as a liquid to the reactor tomaintain the ppm concentration. Temperature was regulated by dualheating and cooling baths. After 180 minutes the reactor wasdepressurised, and the salt and polymer were removed via a dump valve.The polymer was washed with copious distilled water to remove the salt,then dried at 50° C. 282 g of a white polymer powder was recovered.TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Total pressure (bar) 14.3 19 19 14.3 18 14.5 Temperature (° C.) 70 70 7070 65 70 C2 pressure (bar) 12 11.8 10 8 8.5 4 H2/C2 0.0005 0.0005 0.00140.0003 0.00056 0.0006 C6/C2 0.007 0.0061 0.0055 0.007 0.0057 0.0075Production(Kg/h) 1.3 43 39 1 100 0.7

[0201] TABLE 2 Property MFR (2.16 kg) Density (Å) Ea h(500/s) MS (500/s)P (500/s) d(MS)/d(log δ) d(MS/d(P) Polymers (g/10 min) (kg/m{circumflexover ( )}3) Mw/Mn <g>LCB (kl/mol) (Pa · s) (cN) (MPa) (cN) (cN/MPa)Example 1 1.1 920 5.9 0.68 65.1 260 16.7 15.6 9.22 0.81 Example 2 0.3920 5.0 0.74 74.1 290 19.3 17.5 8.62 0.85 Example 3 1.0 923 5.3 0.7767.0 220 16.2 14.4 9.19 0.85 Example 4 0.9 920.3 5.3 0.80 65.4 240 17.714.7 11.10 1.04 Example 5 1.1 917.9 3.6 — 62.4 385 10.0 17.8 5.81 0.50Example 6 1.3 921.4 3.5 — 56.7 400 6.3 18.6 4.03 0.37 Example 7 0.66926.8 3.7 — 66.7 455 5.0 13.7 3.13 0.33 Exceed MLL27MAX 0.85 926 2.31.0  — 690 4.4 32.0 2.11 0.13 Exceed 350D60 1.12 917.7 2.1 — 30.8 7604.0 31.0 1.77 0.11 Dowlex 2045 1.1 919 3.3 — 32.0 580 5.5 23.0 2.00 0.15MOBIL NTA 101 0.84 920 3.4 — 31.0 515 4.8 25.0 2.15 0.16 LL7209AA 0.9920 3.8 — 31.3 570 6.3 24.4 2.85 0.22 LL7206AF 0.6 920 3.9 — 31.0 6009.5 27.0 4.19 0.33 Borealis LE6592 0.15 922.9 11.5 — — 370 15.0 20.06.25 0.70 Affinity FM 1570 1.0 915 2.2 0.92 60.8 570 5.5 24.0 2.64 0.19EBI/Zr(IV)/MAO 0.77 918.3 3.4 0.85 60.2 440 13.0 19.5 7.38 0.59 LD5320AA2.1 921 6.8 0.59 57.8 240 14.5 12.8 11.88 1.05 LD5310AA 1.0 923 7.0 0.5365.3 300 16.6 14.0 8.67 1.07

[0202] Film Tests

[0203] Film was produced from the product of example 2 and LD5310AAusing a Collin single screw film extruder (45 mm, 25L/D) equipped withan LDPE screw and using a temperature profile typical of that used forextrusion of LDPE. The results are summarised in Table 3 together withresults for examples 8-10 which were produced under similar catalyst andpolymerisation conditions to example 2.

[0204] It can be seen that for all of the example polymers that theextrusion behaviour is improved compared to the control LDPE product asjudged by their lower extrusion head pressure, lower motor load andlower specific energy. In addition, this has been achieved for productswith melt indices lower than the conventional LDPE ie products whichmight be expected to show more difficult extrusion behaviour. At thesame time, mechanical properties similar to LDPE or improved have beenobtained.

[0205] Similar film extrusions have been carried out for examples 5 and6 and these are reported in Table 4. For these products, the processingis less advantageous compared to LDPE, as evidenced by the values forhead pressure, motor load and specific energy, but the mechanical areconsiderably better than LDPE and the optical properties are comparable.

[0206] Film Test Methods

[0207] Film dart impact was measured according to ASTM D1709, (Method A)teas strength by ASTM D1922, and tensile properties by ASTM D822. Hazewas measured by ASTM D1003 and gloss by D2457. TABLE 3 Example 2 8 9 10LD5310AA Compounding Machine ZSK53 ZSK58 ZSK58 ZSK58 CaSt ppm 1250 12501250 1250 Irganox 1076 ppm 500 500 500 500 Irgafos PEPQ ppm 800 800 800800 Pellet properties Melt Index g/10 min 0.31 0.32 1.38 0.68 0.9Density Kg/m3 920 922.9 922 919.5 921 121/12 95 84 51 69 62 Filmextrusion Machine Collin Collin Collin Collin Collin Die mm 100 100 100100 100 Die gap mm 0.8 0.8 0.8 0.8 0.8 T° Profil 175/190/ 140/150/140/150/ 140/150/ 140/150/ 195/200/ 160/170/ 160/170/ 160/170/ 160/170/200/200/ 170/170/ 170/170/ 170/170/ 170/170/ 210/210 190/180 190/180190/180 190/180 Screw speed rpm 40 40 41 40 45 Melt pressure bal 151 238166 187 245 Output Kg/h 12 12 12 12 12 Motor Load A 10.7 14.5 11.7 13.913.6 Melt Temp. ° C. 190 165 161 162 163 Haul off rate m/mn 10.2 8.8 119.1 10 BUR 2:1 2:1 2:1 2:1 2:1 Frostline mm 250 160 120 350 120 Specificenergy Kwh/Kg 0.12 0.17 0.14 0.16 0.18 Film properties Thickness um 3838 38 39-41 38 Dart impact g 160 205 103 170 140 MD tens. st. MPa 23.536 break TD tens. st. MPa 24 25 break MD elongation % 520 350 TDelongation % 650 710

[0208] TABLE 4 Example LD5310AA 5 6 Compounding Machine ZSK58 ZSK53 CaStppm 1250 1250 Irganox 1076 ppm 500 500 Irgefos PEPQ ppm 800 800 Pelletproperties Malt Index g/10 min 0.85 0.52 1.29 Density Kg/m3 921 918.3921.4 121/12 61 65.4 40 Film extrusion Machine Collin Collin Collin Diemm 100 100 100 Die gap mm 0.8 0.8 0.8 T° Profil 140/150/160/140/150/160/ 140/150/160/ 170/170/170/ 170/170/170/ 170/170/170/ 190/180190/180 190/180 Screw speed rpm 44 42 42 Melt pressure bal 224 273 297Output Kg/h 12 12 12 Motor Load A 15.3 16.7 17.2 Melt Temp. ° C. 155 153157 Haul off rate m/mn 9.6 9.6 9.3 BUR 2:1 2:1 2:1 Frostline mm 350 350350 Specific energy kWh/Kg 0.19 0.20 0.21 Film properties Thickness um38 38 38 Dart impact g 102 360 252 Haze % 5 10.7 8.1 Gloss o/oo 72 50 61

claims:
 1. A copolymer of ethylene and one or more alpha olefinscontaining from three to twenty carbon atoms said copolymer having: a) along chain branching g′ value of less than or equal to 0.9 and b) avalue of the derivative function δ(MS)/δ(P) of greater than 0.6 whereinMS is the melt strength of the copolymer in cN and P is the extrusionpressure of the copolymer in MPa.
 2. A copolymer as claimed in claim 1wherein g′ is less than or equal to 0.8.
 3. A copolymer as claimed inclaim 1 wherein g′ is in the range 0.5 to 0-9.
 4. A copolymer as claimedin claim 3 wherein g′ is in the range 0.55 to 0.85.
 5. A copolymer asclaimed in claim
 4. wherein g′ is in the range 0.65 to 0.8.
 6. Acopolymer as claimed in claim 1 wherein δ(MS)/δ(P) is greater than 0.65.7. A copolymer as claimed in claim 6 wherein δ(MS)/δ(P) is greater than0.80.
 8. A copolymer as claimed in claim 6 wherein δ(MS)/δ(P) is in therange greater than 0.65 to less than 1.4.
 9. A. copolymer as claimed inclaim 6 wherein δ(MS)/δ(P) is in the range from 0.8 to 1.2.
 10. Acopolymer of ethylene and one or more alpha olefins containing fromthree to twenty carbon atoms said copolymer having: a) a long chainbranching g′ value of less than or equal to 0.9 and b) a value of thederivative function δ(MS)/δ(log{dot over (γ)}) of greater than 7.5wherein MS is the melt strength of the copolymer in cN and {dot over(γ)} is the shear rate of the copolymer in secs⁻¹.
 11. A copolymer asclaimed in claim 10 wherein g′ is less than or equal to 0.8
 12. Acopolymer as claimed in claim 10 wherein g′ is in the range 0.5 to 0.9.13. A copolymer as claimed in claim 12 wherein g′ is in the range 0.55to 0.85.
 14. A copolymer as claimed in claim
 13. wherein g′ is in therange 0.65 to 0.8.
 15. A copolymer as claimed in claim 10 whereinδ(MS)/δ(logy) is greater than 8.0.
 16. A copolymer as claimed in claim10 wherein δ(MS)/δ(log{dot over (γ)}) is from 8.0 to 12.0.
 17. Ahomopolymer of ethylene or a copolymer of ethylene and one or more alphaolefins containing from three to twenty carbon atoms said homopolymer orcopolymer having: a) a value of the derivative function δ(MS)/δ(P) ofgreater than 0.6 and b) an M_(w)/M_(n) value of in the case of thecopolymer less than 8 and in the case of the homopolymer less than 6wherein MS is the melt strength of the copolymer or homopolymer in cNand P is the extrusion pressure of the copolymer or homopolymer in MPaand M_(w)/M_(n) is the ratio of weight average molecular weight tonumber average molecular weight of the copolymer or homopolymer asmeasured by gel permeation chromatography.
 18. A homopolymer orcopolymer as claimed in claim 17 wherein δ(MS)/δ(P) is greater than 0.8.19. A homopolymer or copolymer as claimed in claim 18 wherein δ(MS)/δ(P)is greater than 0.75.
 20. A homopolymer or copolymer as claimed in claim17 wherein δ(MS)/δ(P) is in the range greater than 0.8 to 1.2.
 21. Ahomopolymer or copolymer as claimed in claim 17 wherein the M_(w)/M_(n)value is less than
 6. 22. A homopolymer of ethylene or a copolymer ofethylene and one or more alpha olefins containing from three to twentycarbon atoms said homopolymer or copolymer having: a) a value of thederivative function δ(MS)/δ(log{dot over (γ)}) of greater than 7.5 andb) an M_(w)/M_(n) value of less than 6.5 wherein MS is the melt strengthof the copolymer in cN and {dot over (γ)} is the shear rate of thecopolymer in secs⁻¹ and M_(w)/M_(n) is the ratio of weight averagemolecular weight to number average molecular weight as measured by gelpermeation chromatography.
 23. A homopolymer or copolymer as claimed inclaim 22 wherein δ(MS)/δ(log{dot over (γ)}) is greater than 8.0
 24. Ahomopolymer or copolymer as claimed in claim 22 wherein δ(MS)/δ(logy) isfrom 8.0 to 12.0.
 25. A homopolymer of ethylene or a copolymer ofethylene and one or more alpha olefins containing from three to twentycarbon atoms said homopolymer or copolymer having a long chain branchingg′ value of between about 0.6 and about 0.9.
 26. A homopolymer orcopolymer as claimed in claim 25 wherein g′ is from 0.65 to 0.8.
 27. Acopolymer of ethylene and one or more alpha-olefins containing fromthree to twenty carbon atoms said copolymer having: (a) a long chainbranching g′ value of less than or equal to 0.9 and (b) a value of thederivative function δ(MS)/δ(log {dot over (γ)}) and a M_(w)/M_(n)satisfy the relationship: log[δ(MS)/δ(log {dot over (γ)})]≧0.6log(Mw/Mn)+0.3  wherein Mw/Mn is the ratio of weight average molecularweight to number molecular weight as measured by gel chromatography. 28.A copolymer of ethylene and one or more alpha-olefins containing fromthree to twenty carbon atoms said copolymer having: (a) a long chainbranching g′ value of less than or equal to 0.9 and (b) a value of thederivative function δ(MS)/δ(P) and Mw/Mn which satisfy the relationship:δ(MS)/δ(P)≧0.12 Mw/Mn  wherein Mw/Mn is the ratio of weight averagemolecular weight to number molecular weight as measured by gelchromatography.
 29. A copolymer of ethylene and one or morealpha-olefins containing from three to twenty carbon atoms saidcopolymer having: (a) an flow activation energy, Ea, of value greaterthan or equal to 40 kJ/mol and (b) a value of the derivative functionδ(MS)/δ(log {dot over (γ)}) and a Mw/Mn which satisfy the relationship:log[δ(MS)/δ(log {dot over (γ)})]≧0.6 log(Mw/Mn)+0.3  wherein Mw/Mn isthe ratio of weight average molecular weight to number molecular weightas measured by gel chromatography.
 30. A copolymer of ethylene and oneor more alpha-olefins containing from three to twenty carbon atoms saidcopolymer having: (a) an flow activation energy, Ea, of value greaterthan or equal to 40 kJ/mol and (b) a value of the derivative functionδ(MS)/δ(P) and Mw/Mn which satisfy the relationship: δ(MS)/δ(P)≧0.12Mw/Mn  wherein Mw/Mn is the ratio of weight average molecular weight tonumber molecular weight as measured by gel chromatography.
 31. Acopolymer of ethylene and one or more alpha-olefins containing fromthree to twenty carbon atoms said copolymer having: (a) a long chainbranching g′ value of less than or equal to 0.9 and (b) a value of thederivative function δ(MS)/δ(P) and a flow activation energy Ea satisfythe relationship: Log[δ(MS)/δ(P)]≧3.7−2.4 log(Ea)  wherein Ea ismeasured by dynamic rheometry.
 32. A copolymer of ethylene and one ormore alpha-olefins containing from three to twenty carbon atoms saidcopolymer having: (a) a long chain branching g′ value of less than orequal to 0.9 and (b) a value of the derivative function δ(MS)/δ(log{dotover (γ)}) and a flow activation energy Ea satisfy the relationship:Log[δ(MS)/δ(log{dot over (γ)})]≧2.75−1.25 log(Ea)  wherein Ea ismeasured by dynamic rheometry.
 33. A homopolymer or copolymer as claimedin any one of claims 1, 10, 17, 22, 25, 27-32 obtainable by continuouslypolymerising ethylene alone or with one or more alpha olefins havingfrom three to twenty carbon atoms in the gas phase in a single reactorcontaining a fluidised bed of polymer particles said polymerisationbeing carried out in the presence of a single metallocene catalyst. 34.A homopolymer or copolymer as claimed in claim 33 obtainable bycontinuously polymerising ethylene alone or with one ore more alphaolefins having from three to twenty carbon atoms in the gas phase in areaction system comprising a single reactor containing a fluidised bedof polymer particles, a recycle loop connecting the inlet and outlet ofthe reactor and means for withdrawing the homopolymer or copolymereither continuously or periodically from the reactor whilstpolymerisation is occurring, said polymerisation being carried out inthe presence of a single metallocene catalyst.
 35. A homopolymer orcopolymer as claimed in 33 or claim 34 obtainable by continuouslypolymerising ethylene alone or with one or more alpha olefins havingfrom three to twenty carbon atoms in the gas phase in a single reactorcontaining a fluidised bed of polymer particles said polymerisationbeing carried out in the presence of a single metallocene catalysthaving the following general formula:

wherein M is titanium, zirconium or hafnium, D is a stable conjugateddiene optionally substituted with one or more hydrocarbyl groups, silylgroups, hydrocarbylsilyl groups, silylhydrocarbyl groups or mixturesthereof, said D having from 4 to 40 non-hydrogen atoms and forming aπ-complex with M, Z is a bridging group comprising an alkylene grouphaving 1-20 carbon atoms or a dialkyl silyl- or germanyl group or alkylphosphine or amino radical, R is hydrogen or alkyl having from 1 to 10carbon atoms and x is 1-6.
 36. A homopolymer or copolymer as claimed in33 or claim 34 obtainable by continuously polymerising ethylene alone orwith one or more alpha olefins having from three to twenty carbon atomsin the gas phase in a single reactor containing a fluidised bed ofpolymer particles said polymerisation being carried out in the presenceof a single metallocene catalyst having the following general formula:

wherein M is titanium, zirconium or hafnium in the +2 oxidation state, Dis a stable conjugated diene selected from the group consisting ofs-trans-η⁴,4-diphenyl-1,3-butadiene; s-trans-η⁴-3-methyl-1,3-pentadiene;s-trans-η⁴-1,4-dibenzyl-1,3-butadiene; s-trans-η⁴-2,4-hexadiene;s-trans-η⁴-1,4-ditolyl-1,3-butadiene;s-trans-η⁴-1,4-bis(trimethylsilyl)-1,3-butadiene;scis-η⁴-1,4-diphenyl-1,3-butadiene; s-cis-η⁴-3-methyl-1,3-pentadiene;s-cis-η⁴-2,4-hexadiene; s-cis-η⁴2,4-hexadiene; s-cis-η⁴1,3-pentadiene;s-cis-η⁴-1,4-ditolyl-1,3-butadiene; ands-cis-η⁴-1,4-bis(trimethylsilyl)-1,3-butadiene, said s-cis diene groupforming a π-complex as defined herein with the metal. Z is a bridginggroup comprising an alkylene group having 1-20 carbon atoms or a dialkylsilyl- or germanyl group or alkyl phosphine or amino radical, R ishydrogen or alkyl having from 1 to 10 carbon atoms and x is 1-6.
 37. Ahomopolymer or copolymer as claimed in 33 or claim 34 obtainable bycontinuously polymerising ethylene and, in the case of copolymerising,one ore more alpha olefins having from three to twenty carbon atoms inthe gas phase in a single reactor containing a fluidised bed of polymerparticles said polymerisation being carried out in the presence of asingle metallocene catalyst having the following formula:


38. A film exhibiting a dart impact value measured by ASTM D-1709(Method A) in the range about greater than 100 and up to about 2000comprising a copolymer as claimed in claims 1, 10, 17, 22, 25, 27-32.39. A film exhibiting a dart impact value measured by ASTM-D1709 (MethodA) in the range about greater than 100 and up to about 2000 comprising acopolymer of ethylene and an alpha-olefin of from 3 to 10 carbon atomswhich has a density of from 0.910-0.930, a I₂₁/I₂ value of ≧35, a longchain branching g′ value of less than or equal to 0.9 and a value of thederivative function δ(MS)/δ(P) of greater than 0.6.
 40. A filmexhibiting a dart impact value measured by ASTM-D 1709 (Method A) in therange about greater than 100 and up to about 2000 comprising a copolymerof ethylene and an alpha-olefin of from 3 to 10 carbon atoms which has adensity of from 0.910-0.930, a I₂₁/I₂ value of ≧35, a long chainbranching g′ value of less than or equal to 0.9 and a value of thederivatie function δ(MS)/δ(P) and flow activation energy Ea satisfy therelationship log[δ(MS)/δ(P)]≧3.7−2.4 log(Ea).